Draft: Run only e2e tests if MR changes only e2e tests

What does this MR do?

This is the first iteration of https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/564

In this MR, we fetch all the files that have changed in an MR and filter by qa/specs/features and save them to QA_TESTS variable. If there are files other than the filtered ones, save empty result so that the entire suite will run.

We will still run all the jobs but some jobs might not run any examples.

In the second iteration, we will try to eliminate the jobs that would not run any examples.

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.